A fuel cell has been proposed as a clean, efficient and environmentally responsible power source for electric vehicles and various other applications. Individual fuel cells can be stacked together in series to form a fuel cell stack for various applications. The fuel cell stack is capable of supplying a quantity of electricity sufficient to power a vehicle. In particular, the fuel cell stack has been identified as a potential alternative for the traditional internal-combustion engine used in modern automobiles.
One type of fuel cell is the polymer electrolyte membrane (PEM) fuel cell. The PEM fuel cell includes three basic components: an electrolyte membrane; and a pair of electrodes, including a cathode and an anode. The electrolyte membrane is sandwiched between the electrodes to form a membrane-electrode-assembly (MEA). The MEA is typically disposed between porous diffusion media which facilitates a delivery of reactants, such as hydrogen to the anode and oxygen to the cathode. The porous diffusion media are sometimes referred to as gas diffusion media or gas diffusion layers. In the electrochemical fuel cell reaction, the hydrogen is catalytically oxidized in the anode to generate free protons and electrons. The protons pass through the electrolyte to the cathode. The electrons from the anode cannot pass through the electrolyte membrane, and are instead directed as an electric current to the cathode through an electrical load, such as an electric motor. The protons react with the oxygen and the electrons in the cathode to generate water.
It is also known to use other reactants in the PEM fuel cell such as methanol, for example. Methanol may be catalytically oxidized to form carbon dioxide. Protons from the methanol oxidation are transported across the electrolyte membrane to the cathode where they react with oxygen, typically from air, to generate water. As with the hydrogen PEM fuel cell, electrons are transported as an electric current through the external load, such as the electric motor, from the anode to the cathode.
The diffusion media is typically formed from a porous material adapted to perform a multifunctional role in the fuel cell. It is known to manufacture the diffusion media from carbon paper, such as TGP-H-030 commercially available from Toray Industries, Inc., for example. Carbon paper is typically suitable for distributing reactants, gaseous or otherwise, to the electrodes of the fuel cell. The diffusion media also conducts electrons and transfers heat generated at the MEA to a coolant. With respect to water management of the fuel cell, the diffusion media transports water produced by the electrochemical fuel cell reaction away from the PEM. The water management capability of the diffusion media is critical to any optimization of fuel cell performance. The diffusion media may further include a microporous layer that provides a transition layer between the electrodes and the diffusion media and facilitates the water removal from the PEM.
Alternative types of porous materials have been described by Jacobsen et al. in “Compression behavior of micro-scale truss structures formed from self-propagating polymer waveguides”, Acta Materialia 55, (2007) 6724-6733, the entire disclosure of which is hereby incorporated herein by reference. One method and system of creating polymer materials with ordered microtruss structures is disclosed by Jacobsen in U.S. Pat. No. 7,382,959, the entire disclosure of which is hereby incorporated herein by reference. The system includes at least one collimated light source selected to produce a collimated light beam; a reservoir having a photo-monomer adapted to polymerize by the collimated light beam; and a mask having at least one aperture and positioned between the at least one collimated light source and the reservoir. The at least one aperture is adapted to guide a portion of the collimated light beam into the photo-monomer to form the at least one polymer waveguide through a portion of a volume of the photo-monomer. Microtruss materials produced by the method and system are further disclosed by Jacobsen in U.S. patent application Ser. No. 11/801,908, the entire disclosure of which is hereby incorporated herein by reference. A polymer material that is exposed to radiation and results in a self-focusing or self-trapping of light by formation of polymer waveguides is also described by Kewitsch et al. in U.S. Pat. No. 6,274,288, the entire disclosure of which is hereby incorporated herein by reference.
There is a continuing need for a structure and method of manufacturing fuel cell diffusion media that optimizes fuel cell durability, minimizes tooling costs, minimizes production costs, and minimizes development time.